The Compensatory Sleep Response (CSR; characterized by increased sleep time and depth) that is seen in mice after a period of total sleep deprivation (TSD) indicates that sleep is a homeostatic process. The mechanism for this homeostatic drive is unknown, but is likely to be involved in the etiology of some sleep disorders. We have found that similar to TSD, methamphetamine, an inhibitor of the cell membrane dopamine (DA) transporter (DAT) and of the intracellular DA transporter (VMAT2), produces sleep loss followed by a CSR in mice. In contrast the DAT-specific inhibitor GBRI2909 produces sleep loss without a subsequent CSR. In light of these observations we theorize that intracellular DA stores play a critical role in sleep homeostasis. This proposal addresses three issues relevant to this theory. Is the wake promoting effect GBR12909 mediated exclusively through inhibition of DAT9? Are the wake promoting effect of methamphetamine and the subsequent CSR mediated through inhibition of DAT and of intracellular DA stores? Do genetic alterations of cell membrane (DAT) and vesicular (VMAT2) DA transporters alter CSR to TSD? We propose a targeted molecular genetic approach to address these questions. To determine the molecular sites of action of GBRI2909 and methamphetamine, we will study the effects of these drugs on sleep in mice with genetic alterations of DAT and VMAT2 expression. To determine the role of DAT and VMAT2 in physiological sleep in the absence of pharmacological manipulation, we will also study the CSR to TSD in these genetically engineered mice.